During the late afternoon and early evening hours on April 3rd (Tuesday), a strong area of low pressure was centered over eastern Indiana and western Ohio. A strong cold front extended southwest from this area of low pressure into central Arkansas and eastern Texas. Ahead of this front, strong to severe thunderstorms developed during the afternoon hours on Tuesday closer to the parent low near the Ohio Valley. During the evening hours on Tuesday, as the parent surface low moved northeast into the Great Lakes region, the better helicity, shear, and upper level lapse rates shifted further northeast as well.
However, due to very warm temperatures in the 80 to 85 degree range that were reached during the afternoon, strong low/mid level lapse rates and surface based instability between 500 and 1000 J/kg was in place near and west of I-65 around 7 PM. This was in place ahead of a second line of strong to severe storms that formed from earlier convection in eastern Arkansas and western Mississippi. As this line (which was aided by a 40 to 50 knot low level jet, 100 knot upper level jet, and dry air entrainment near the surface) pushed east into an unstable but weakly sheared environment, it held together and produced widespread damaging winds across much of northern Alabama, including some gusts up between 70 and 75 mph in the Huntsville and Decatur areas after 9 PM. This line weakened as moved east of interstate I-65 and moved out of northeastern Alabama shortly after midnight on Tuesday, but still produced areas of damaging winds in those areas as well.
|